1. Field of the Invention
This invention relates to a metallic container having a circumferential bonded portion and a process for its production. More specifically, this invention relates to a metallic container composed of a first and a second section each composed of a metallic cup-like fabricated article having a primer coating, the two sections being lap-bonded at their circumferential open end portions by means of a thermoplastic film-like adhesive, and to a process for producing said metallic container.
2. Description of the Prior Art
Japanese Laid-Open Patent Publications Nos. 49611/1979, 32228/1981 and 38294/1980 disclose that metallic containers having a circumferential bonded portion produced by bonding two metallic cup-like fabricated articles having nearly equal diameters and a relatively small thickness with an adhesive are suitable for use as pressure cans for beer and carbonated beverages.
The two metallic cup-like fabricated articles constituting the metallic containers are produced usually by drawing a metallic blank having a corrosion-resistant coating on that surface which is to become the inner surfaces of these cup-like shaped articles. Hence, the inside surfaces of these metallic cup-like shaped articles are protected by the corrosion-resistant coating, but the metal substrate is exposed at the end surfaces at the open end portions formed by cutting. To secure corrosion resistance of the metallic container against the contents, therefore, it is desirable to coat particularly the end surface of the open end portion of the inside of the cup-like fabricated article and its inner circumferential surface near the end surface with an adhesive layer.
The adhesive layer may be formed, for example, by the coating of a thermosetting adhesive or a slurry-type adhesive disclosed, for example, in Japanese Laid-Open Patent Publication No. 153629/1980, or electrostatic coating of a powdery adhesive. In order to easily obtain an adhesive layer having a uniform thickness and being free from defects such as the occurrence of pores, it is preferred to use a thermoplastic film-like adhesive and apply it so as to envelop the end surface having the exposed metal substrate.
To secure corrosion resistance, considered, it is very important for the film-like adhesive to completely cover the end surface having the exposed metal substrate. If even a part of the metal substrate is exposed, the metal will dissolve from this part into the contents of the metallic container and extremely damage the taste and flavor of the contents. Furthermore, metal corrosion tends to spread beneath the protective coating starting at the exposed part. Hence, the adhesion of the protective coating is reduced, and the strength of the bonded portion becomes extremly weak. When corrosion is heavy, leakage from that part occurs or holes form in the container.